The present invention relates to a planar antenna which is extremely small in dielectric loss and conductive loss. More in detail, the present invention relates to a planar antenna which comprises a dielectric layer containing a homopolymer of 3-methylbutene-1 or a copolymer of 3-methyl-butene-1 and an alpha-olefin of from 2 to 12 carbon atoms and/or a polyene, a conductor laminated on the back surface of the dielectric layer, and a circularly polarized radiation microstrip element formed from a metal foil and provided on another surface of the dielectric layer, and to a method for producing a planar antenna, which method comprises the steps of interposing a dielectric layer containing a homopolymer of 3-methylbutene-1 or a copolymer of 3-methylbutene-1 and an alpha-olefin of from 2 to 12 carbon atoms and/or a polyene between a conductor and a metal foil, molding the thus formed laminate by thermal pressing at a temperature of from 280.degree. to 330 .degree. C. under a pressure of from 40 to 50 kg/cm.sup. 2, and etching the metal foil on the surface of the dielectric substrate, thereby forming a microstrip element circuit.
The planar antenna has been developed for receiving satellite broadcasting wave and has a merit of not being substantially influenced by snow, wind pressure, etc. as compared to the parabola antenna. However, at present, there is a problem in the planar antenna in that the gain is little.
Hitherto, for the dielectric substrate for the planar antenna, a fluorocarbon resin, glass fibers and a cross-linked polyethylene have been used as the dielectric substrate. However, from the viewpoint of the high price and the large dielectric loss of the materials, the improvement thereof has been necessitated.
On the other hand, connectors, printed circuit board, metal-plated plastics used for magnetic recording material, and durable composite material such as packaging material and bottles containing 3-methylbutene-1 have been known. For instance, a molded article produced by providing a thin metal layer on a homopolymer of 3-methylbutene-1 or a copolymer of 3-methylbutene-1 and an alpha-olefin of from 2 to 12 carbon atoms and/or a polyene [refer to Japanese Patent Application Laid-Open (KOKAI) No. 60-116764 (1985)]and a laminate produced by providing a thermoplastic resin layer or a metal layer on at least one of the surfaces of a sheet-form material made of a homopolymer of 3-methylbytene-1 or a copolymer of 3-methylbutene-1 and another alpha-olefin and/or a polyene [refer to Japanese Patent Application Laid-Open (KOKAI) No. 61-69452 (1986)]may be mentioned.
The present inventors have found that the high-frequency characteristics which have not been obtained by the conventional dielectric substrate for the planar antenna can be obtained by the use of a resin composed of a homopolymer of 3-methylbutene-1 or a copolymer of 3-methylbutene-1 and an alpha-olefin of from 2 to 12 carbon atoms and/or a polyene as the dielectric layer, and based on the finding, the present invention has been attained.